In image display devices such as cathode ray tube (CRT) display devices, liquid crystal displays (LCD), plasma displays (PDP), and electroluminescence displays (ELD), generally, an antireflection optical layered body is provided on the outermost surfaces thereof. Such an optical layered body for antireflection inhibits the reflection of images or decreases a reflectance by virtue of scattering or interference of light.
As one of such antireflection optical layered bodies, an antiglare layered body, in which an antiglare layer having a surface roughness is formed on the surface of a transparent substrate, is known. Such an antiglare layered body can prevent the reduction in visibility due to reflection of external light or reflection of images by scattering external light through a surface roughness of the surface. As an antiglare layered body, a layered body in which a surface roughness is formed with particles (Patent Document 1), and a layered body in which a surface roughness is formed by performing an emboss molding treatment (Patent Documents 2 and 3) are known.
In recent years, with an increase of high definition panel resolution, performance required of the optical layered body has been increased. It is thought that an antiglare layered body used for such high definition panels requires a fine surface roughness. That is, by having the fine surface roughness, the aim is a response to high definition panels. The antiglare layered body having such a fine surface roughness can respond to requirements of high definition panel resolution, however it has pointed to have problems that the image display face looks white (whitening) or contrast is deteriorated.
Further, if such a an antiglare layered body is applied to the surface of an image display device such as a personal computer, there is a problem that “scintillation”, that is, a state in which when transmitting light from a back side such as a backlight in a display passes though a rough surface of an antiglare layered body formed at the outermost surface of a panel, this light disturbs displayed pixels because the surface roughness of the antiglare layered body is apt to act as a fine lens.
As a method of solving “scintillation”, a technique of increasing a density of peaks and valleys of the surface for the purpose of enhancing sharpness, a technique of imparting an internal scattering effect to the antiglare layered body by adding scattering particles having a difference in refractive indexes with a resin composing the antiglare layer and the like are known.
However, such a method of solving “scintillation” is a method causing surface whitening or white cloud due to an internal scattering effect by a high density of peaks and valleys of the surface. Particularly in the method of increasing a density of peaks and valleys of the surface, scattering due to external light reflection is increased and whitening increases. Therefore, the antiglare property is good, but this method would be a factor that deteriorates contrast. That is, in conventional antiglare layered bodies, it was difficult to satisfy all of “antiglare property”, “improvement of contrast”, and “scintillation prevention”. Therefore, there may be cases where these antiglare layered bodies are inferior in black color reproducibility including gloss blackness (clear and gloss black color), contrast and the like in a screen display. That is, there may be cases where a difference in gradation of black color is hardly recognized and sensitivity is low in expression of black color tone, particularly in low tone, in a bright room. Specifically, there may be cases where in color recognition between black and gray, sometimes color blur occurs or color tone could not be recognized and recognized as black of the same tone. In the antiglare layered bodies having a good antiglare property=scattering performance of external light, these visibility was significantly deteriorated.
On the other hand, in the antireflection method of based on light interference, techniques of imparting a function by controlling a refractive index or a layer thickness of each layer, such as a method in which a refractive index of a hard coat layer having a clear and smooth outermost surface is increased and a low refractive index thin film is provided on the hard coat layer, are known. In this method, the above-mentioned contrast is good, and the reflection of external substances in a surface of a display screen can be prevented by lowering (e.g., reflection Y value 0.1 to 0.8%) the reflectance without limit. However, this method has difficulties of controlling a layer thickness of a coat and has many problems in terms of production, and most of materials are expensive. Further, if the reflectance is lowered through light interference, interference color is produced, and therefore there was a problem that this interference color discolors white or black color in a screen reddish or bluish even though the reflectance is low. Further, when the reflectance is not so low, prevention of the reflection was sometimes difficult. Furthermore, it has been emerged that even though the reflectance is extremely low, the reflection cannot be prevented depending on an environment in which television is watched. For example, in an interior with white wall, the white wall is reflected as white on the surface of a screen as long as the surface is flat.
Accordingly, currently, developments of an optical layered body which can prevent scintillation of an image surface effectively and achieve black color reproducibility, particularly gloss blackness are desired, and particularly, an optical layered body which can be used for not only liquid crystal displays (LCD) but also other applications such as cathode ray tube (CRT) display devices, plasma displays (PDP), fluorescent display tubes and field emission displays is desired.    Patent Document 1: Japanese Kokai Publication Hei-6-18706    Patent Document 2: Japanese Kokai Publication Hei-6-16851    Patent Document 3: Japanese Kokai Publication 2004-341070